The present invention relates to a cathode material comprising a lithium composite oxide including lithium (Li), a first element including at least two kinds selected from the group consisting of manganese (Mn), nickel (Ni) and cobalt (Co), and a second element including at least one kind selected from the group consisting of aluminum (Al), titanium (Ti), magnesium (Mg) and boron (B), and a battery using the same.
In recent years, with advances in electronic technologies, higher performance, downsizing and portability of electronic devices have dramatically progressed. Accordingly, studies of rechargeable secondary batteries as power sources which can be conveniently and economically used for a long time have been progressing. As the secondary batteries, lead-acid batteries, alkaline batteries, lithium-ion secondary batteries and so on are conventionally and widely known. Among them, attention has been given to the lithium-ion secondary batteries as batteries in which higher power and higher energy density can be achieved.
In the lithium-ion secondary battery, as a cathode material, for example, a metal oxide, a metal sulfide or a polymer is used. More specifically, a compound not including lithium such as TiS2, MoS2, NbSe2, V2O5 or the like, or a lithium composite oxide including lithium such as LiCoO2, LiNiO2, LiMnO2, LiMn2O4 or the like is known.
Among them, LiCoO2 is widely applied to practical use as a cathode material having a potential of approximately 4 V relative to a lithium metal potential, and is an ideal cathode material in various aspects because LiCoO2 has a higher energy density and a higher voltage. However, Co (cobalt) as a resource is unevenly distributed and scarce, so there is a problem that it is difficult to stably supply Co, thereby a material cost becomes higher.
Therefore, instead of LiCoO2, a lithium composite oxide including abundant and low-cost nickel (Ni) or manganese (Mn) as a base holds promise.
However, LiNiO2 has a large theoretical capacity and a high discharge potential, but its crystalline structure collapses in accordance with the progress of a charge-discharge cycle, thereby resulting in a decline in a discharge capacity and lower thermostability.
Moreover, LiMn2O4 with a normal spinel structure and a space group Fd 3 m has as high a potential as LiCoO2, and can obtain a high battery capacity. Further, LiMn2O4 can be easily synthesized. However, there is a problem such as insufficient stability or insufficient cycle characteristics, that is, degradation in capacity is large during storage at high temperature, and Mn is dissolved in an electrolyte solution.
Moreover, LiMnO2 with a layer structure can obtain a higher capacity than LiMn2O4, however, it is difficult to synthesize LiMnO2, and there is a problem that when a charge-discharge cycle is repeated, the structure becomes unstable, and the capacity declines.
In view of the foregoing, it is an object of the present invention to provide a cathode material capable of achieving a higher discharge capacity and a higher discharge voltage and obtaining superior charge-discharge characteristics, and a battery using the cathode material.